Describe the by Serum Sodium of Types of Dehydration.

Definition

Depending on the relative losses of water and sodium, dehydration is classified by the serum sodium into three types, each with distinct clinical features and correction principles.

Isonatraemic Dehydration (na 130–150 Mmol/l)

• The commonest type (~70%); proportionate loss of water and sodium.
• Loss is mainly from the ECF → classic signs (sunken eyes, poor skin turgor); corrected with isotonic fluids over 24 hours.

Hyponatraemic Dehydration (na < 130 Mmol/l)

• Sodium loss exceeds water loss (e.g. Replacing diarrhoea losses with plain water).
• Water shifts from ECF → ICF → greater circulatory compromise (earlier shock) for the same fluid loss.
• May cause lethargy, seizures; correct sodium slowly to avoid osmotic demyelination.

Hypernatraemic Dehydration (na > 150 Mmol/l)

• Water loss exceeds sodium loss (high fever, high solute feeds, inadequate water intake).
• Water shifts ICF → ECF, so skin turgor is relatively preserved; the skin feels 'doughy', the child is irritable with a high-pitched cry, and there is a risk of seizures and intracranial bleeding.
• Correct slowly over ~48 hours (a fall in Na of ≤ 0.5 mmol/L/hr) to avoid cerebral oedema.

Clinical Estimation of Sodium Type

• The type cannot be told from the degree of dehydration alone — it needs a serum sodium.
• Suspect hypernatraemia in a very irritable child with doughy skin and preserved circulation despite obvious fluid loss, and hyponatraemia when shock appears out of proportion to the apparent fluid loss.

Hypernatraemic dehydration must be corrected slowly.